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Wave Optics
Question
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Monochromatic light of frequency 6.0 x 1014 Hz is produced by a laser. The power emitted is 2 x 10-3 W. The number of photons emitted, on the average, by the source per second is:

  • 5 x 1015

  • 5 x 1016

  • 5 x 1017

  •  5 x104

Answer

A.

5 x 1015

Photons are the packets of energy. Power emitted ,
P = 2 x 10-3 W
Energy of photon, 
E = hv 
 = 6.6 x 10-34 x 6 x 1014 J
h being planck's constant.
Numer of photons emitted per second
n = P/E
=  2 x 10-3 / 6.6 x 10-34 x 6 x 1014
 = 5 x 1015

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